Conventional gas chromatography

The power of the system to overcome the problems associated with coeluting compounds is demonstrated in conjunction with the use of deuterated (or13C-labelled compounds) as internal standards. Such techniques could not be used in conventional gas chromatography as the deuterated compounds often co-elute, making quantification difficult if not impossible. With the ion-trap detector, however, it is easily possible to differentiate between the ions arising from the different compounds and the intensities of these ions could then be used for quantification of the compounds involved. The application of such techniques can be shown by... 

Arakawa et al. [96] have pointed out that methyltin compounds may be extracted from complex matrices and analysed by conventional gas chromatography. However, the procedure is lengthy, involving multiple steps where speciation may be altered and vessel adsorption effects may be large. Detection limits achievable with a flame ionization detector are 10-100pg [97],... 

Conventional gas chromatography (GC) based on the use of chiral stationary phases can handle only a few dozen ee determinations per day. In some instances GC can be modified so that, in optimal situations, about 700 exact ee and E determinations are possible per day [29]. Such meclium-throughputmay suffice in certain applications. The example concerns the lipase-catalyzed kinetic resolution of the chiral alcohol (R)- and (S)-18 with formation of the acylated forms (R)- and (S )-19. Thousands of mutants of the lipase from Pseudomonas aeruginosa were created by error-prone PCR for use as catalysts in the model reaction and were then screened for enantioselectivity [29]. 

Figure 14.5. Fatty acids patterns of soils under long-term monoculture, (a) Lipid extract of soil under maize, unfertilized, after derivatization with tetramethylammonium hydroxide determined by conventional gas chromatography/mass spectrometry (GC/MS) in comparison to direct, in-source pyrolysis-field ionization mass spectrometry (Py-FIMS) without derivatization (Jandl et al., unpublished), (b) Py-FIMS of lipid extract of soil under rye, farmyard manure (FYM) treatment, compared to solid extraction residue, both directly measured without derivatization. Reprinted from Marschner, B., Brodowski, S., Dreves, A., et al. (2008). How relevant is recalcitrance for the stabilization of organic matter in soils Journal of Plant Nutrition and Soil Science 171, 91-110, with permission from Wiley-VCH.

If the desorption rate is sufficiently large, chromatographic separation and analyses of mixed suspensions become possible. Dependence of adsorption and desorption rates upon particle properties causes some components of a pulse of mixed particles carried through a packed bed to be eluted more quickly than others. This mechanism is analogous to conventional gas chromatography, and all the formalisms developed for the latter may be applied. 

The amount of adsorbed gas can be measured either gravimetrically or volumetrical-ly, and a variety of types of apparatus have been designed and used. A continuous procedure may also be used. In this method a nonadsorptive carrier gas, such as helium, is passed through the sample at a known rate with varying concentrations of nitrogen introduced in stages. The amount adsorbed can be determined by conventional gas chromatography. 

Inverse gas chromatography (IGC) refers to the characterization of the chromatographic stationary phase (polymer) using a known amount of mobile phase (solvent). The stationary phase is prepared by coating an inert support with polymer and packing the coated particles into a conventional gas chromatography column. The activity coefficient of a given solvent can be related to its retention time on the column. The equipment itself is commercially available, easily automated, and extremely versatile. 

The abuse of cannabis cannot be detected by thin-layer Chromatography or by conventional gas Chromatography because the concentrations of cannabinoids in urine are too low. Immunoassay, applied to either blood or urine, is the best method (see B. Law et ah, J. analyt. Toxicol., 1984, <5, 14-... 

Prabhakar et al. [56] developed and validated six HPLC assay methods which permitted resolution of tailing problems for the separation of phenothiazine bioactive components and preservatives in liquid pharmaceutical formulations by using cyano-, C-8, C-18, and cation-exchange phases. The mass spectrometry (MS) of phenothiazines in biological samples is important in forensic analysis. However, since most phenothiazines having long piper-azinyl side chains are thermolabile, the phenothiazines are not suitable for conventional gas chromatography (GC)/MS analysis. Therefore, a system of capillary HPLC/fast atom bombardment-mass spectrometry (FAB-MS) was... 

The technique involves creating within a column a stationary phase of the solid material of interest. The stationary phase may be a thin polymeric coating on an inert substrate, a finely divided solid, or a thin polymeric coating on the column wall. A volatile probe of known characteristics is passed through the column via an inert mobile phase and the output is monitored. The residence time of the probe and the shape of the chromatogram indicate the characteristics of the stationary phase and its interaction with the probe. Thus, IGC is a variation of conventional gas chromatography. 

Nersesyants et al. [91] were successful in using this method for the separate determination of aluminium and aluminium carbide. A solid sample was treated with an acid, and the gas evolved was collected in a gas volume-measuring device. The gas composition was determined on a column containing molecular sieves by conventional gas chromatography. The hydrogen content is proportional to that of the metal in the sample, and the content of the organic gaseous component corresponds to that of the carbide [91]. 

The reaction products were analyzed by conventional gas chromatography using 20% Apiezon grease or 5% Silicone OV-17 packings (Kogyo Inc.), and acenaphthene was used as an internal standard. The reaction products were identified by comparing their retention times with those obtained for known samples. The simple Hiickel calculations were performed on a microcomputer (NEC Corporation model PC-9801VM2). 

Capillary supercritical fluid chromatography (SFC) ( ) has characteristics fitting between those of conventional gas chromatography (GC) and high performance liquid chromatography (HPLC) (2). 

Inverse gas chromatography (IGC) is a method very well used by the adhesion community for obtaining thermodynamic and morphological information on a variety of materials such as fillers, pigments, colloids, fibers, powder, wood, and polymers [17,60,61,85-94]. The term inverse means that the stationary phase is of interest by contrast to conventional gas chromatography in which the mobile phase is of interest. Its success lies in the fact that it is simple, versatile, usable over a very wide range of temperature, and very low cost. IGC has a well established background for the assessment of yg acid-base parameters for polymers and fillers. Such thermodynamic parameters can be further used to estimate the reversible work of adhesion at polymer-fiber and polymer-filler interfaces [95,96],... 

Trichloroethanol in Urine by Head-space Gas Chromatography and Conventional Gas Chromatography Mitteilungsbl. GDCh. (Ges. Deut. 

For the reasons outlined above, alternative methods were developed that avoid the measurement of absolute vapor pressures. One procedure combines head space sampling with conventional gas chromatography (HS-GC) [31] and yields relative vapor pressures, normalized to the vapor pressure of the pure solvent. A well-defined volume of the equilibrium gas phase is taken out from a thermostated vial... 

In a typical IGC experiment, the apparatus used is similar to that used in conventional gas chromatography. The test solute, which has known properties, is injected at the inlet of the column, which may be either of two forms ... 

Because the stationary phase is the phase of interest (in contrast to conventional gas chromatography), this process is termed inverse gas chromatography. The physico-chemical properties of the examined material are deduced from the retention data of a series of carefully selected test solutes [7]. 

The principles of IGC, as a gas-phase technique used to characterize the surface and bulk properties of solid materials, are very simple as the process is the reverse of conventional gas chromatography. Typically, an empty cylindrical column is uniformly packed with the solid material of interest, normally a powder, fiber, or film. A pulse or constant concentration of gas is then injected down the column at a fixed carrier gas flow rate, and the retention behavior of the pulse or concentration front is measured with a detector (Figure 10.1). The retention of a solvent or probe molecule on the material is recorded and the measurement is made effectively at an inflnite dilution of the probe. A range of thermodynamic parameters can then be calculated. A major advantage of IGC is that it is readily applicable to mixtures of two or more polymers. 

Example 7.1.6 In conventional gas chromatography, the typical quantity measured for species i is the retention time fj), under given conditions. To develop an estimate of the number of plates N in the chromatographic column of length L, one also needs to determine the standard deviation [Pg.540]

---